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| Probabilistic Tornado Graphic | |||||||||
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| Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point. |
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| Probabilistic Damaging Wind Graphic | |||||||||
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| Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point. |
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| Probabilistic Large Hail Graphic | |||||||||
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| Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point. |
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SPC AC 091620 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1120 AM CDT MON SEP 09 2013 VALID 091630Z - 101200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER MIDWEST/UPPER GREAT LAKES... ...SYNOPSIS... AN UPPER HIGH CENTERED OVER THE MID MS VALLEY WILL FLATTEN/ELONGATE WHILE EDGING EWD INTO THE OH/TN VALLEYS. THIS IS IN RESPONSE TO THE EWD PROGRESSION OF A DE-AMPLIFYING SHORT-WAVE TROUGH WHICH WILL SHIFT FROM THE NRN HIGH PLAINS AND SRN CANADA PRAIRIE PROVINCES TOWARD THE UPPER GREAT LAKES. ELSEWHERE...AN UPPER LOW WILL REMAIN QUASI-STATIONARY OVER THE LOWER CO VALLEY. IN THE LOW LEVELS...A SURFACE CYCLONE ASSOCIATED WITH THE NRN HIGH PLAINS TROUGH WILL DEVELOP EWD ALONG A POLEWARD-MOVING WARM FRONT FROM ERN ND TO THE ERN U.P. OF MI/NRN LAKE HURON BY TUESDAY MORNING. MEANWHILE...A TRAILING COLD FRONT WILL PROGRESS SEWD THROUGH THE NRN PLAINS AND UPPER MS VALLEY INTO THE UPPER GREAT LAKES...MID MO VALLEY...AND CNTRL HIGH PLAINS BY 10/12Z. ...UPPER MIDWEST/UPPER GREAT LAKES THIS AFTERNOON INTO TONIGHT... CONSIDERABLE CLOUDINESS IS PRESENT ACROSS THE REGION THIS MORNING OWING TO A BROAD ZONE OF WAA/ISENTROPIC ASCENT TO THE NORTH OF THE WARM FRONT...AND IN ASSOCIATION WITH A RECENTLY DECAYED NOCTURNAL MCS WHICH FORMED LAST NIGHT OVER THE DAKOTAS. MOREOVER...THE 12Z ABR AND OMA SOUNDINGS SHOWED THE PRESENCE OF A PRONOUNCED EML AND ASSOCIATED CAP WHICH WILL BE ADVECTED NEWD TODAY IN ADVANCE OF THE MIDLEVEL TROUGH. THESE FACTORS WILL LIKELY DELAY ANY POTENTIAL FOR STORM DEVELOPMENT UNTIL CLOSER TO 10/00Z. AT THIS TIME... SURFACE-BASED OR NEAR-SURFACE-BASED TSTM INITIATION APPEARS MOST PROBABLE INVOF THE SURFACE TRIPLE POINT OVER E-CNTRL/NERN MN INTO NRN WI AS FORCING FOR ASCENT IS POSSIBLY ENHANCED BY A WEAK IMPULSE PRECEDING THE PRIMARY UPPER SYSTEM. SHOULD STORMS BECOME ROOTED WITHIN THE BOUNDARY LAYER...THE LOCAL ENVIRONMENT WILL BE QUITE FAVORABLE FOR SUPERCELLS OWING TO THE PRESENCE OF MODERATE TO STRONG INSTABILITY /MLCAPE OF 2000-3000 J PER KG/ WHICH WILL ALIGN WITH ENHANCED LOW-LEVEL AND DEEP-LAYER SHEAR ALONG THE WARM FRONT. AN ATTENDANT RISK FOR A COUPLE TORNADOES...LARGE HAIL...AND DAMAGING WINDS WOULD EXIST WITHIN THE FIRST FEW HOURS OF INITIATION. THEREAFTER...COALESCING STORM-SCALE COLD POOLS AND THE DEVELOPMENT OF A 40-50 KT NOCTURNALLY ENHANCED LLJ WILL BE SUPPORTIVE OF UPSCALE GROWTH INTO A FORWARD-PROPAGATING MCS WITH A CONTINUED RISK FOR MAINLY DAMAGING WINDS. ...CNTRL HIGH PLAINS THIS AFTERNOON AND EVENING... WHILE LARGE-SCALE FORCING FOR ASCENT WILL REMAIN NEGLIGIBLE THROUGH THE PEAK OF THE DIURNAL HEATING CYCLE...STRONG BOUNDARY LAYER HEATING AND CONVERGENCE ALONG THE COLD FRONT --AS WELL AS POST-FRONTAL UPSLOPE OVER SERN WY/NERN CO-- MAY BE SUFFICIENT TO INITIATE ISOLATED TO WIDELY SCATTERED STORMS. GIVEN THE PRESENCE OF A DEEP...WELL-MIXED BOUNDARY LAYER AND MODEST AMOUNTS OF INSTABILITY AND VERTICAL SHEAR...A FEW SEVERE STORMS ARE POSSIBLE WITH A RISK FOR LOCALLY DAMAGING WIND GUSTS AND PERHAPS SOME HAIL. ...ND THIS AFTERNOON... RESIDUAL BOUNDARY LAYER MOISTURE AND COOLING TEMPERATURES ALOFT WILL CONTRIBUTE TO MODEST AIR MASS DESTABILIZATION TODAY ALONG AN INVERTED TROUGH OR WEAK OCCLUDED FRONT. DEEP-LAYER FORCING FOR ASCENT AHEAD OF THE MIDLEVEL TROUGH ALONG WITH LOW-LEVEL UPLIFT ALONG THE SURFACE BOUNDARY MAY BE SUFFICIENT TO SUPPORT A FEW INTENSE STORMS CAPABLE OF ISOLATED OCCURRENCES OF WIND AND HAIL. ...LOWER CO VALLEY THIS AFTERNOON AND EVENING... DEEP-LAYER FORCING FOR ASCENT ASSOCIATED WITH THE MIDLEVEL VORTICITY MAXIMUM WILL COMBINE WITH A VERY MOIST AIR MASS /I.E. PW VALUES APPROACHING TWO INCHES/ TO FOSTER SCATTERED TO NUMEROUS STORMS TODAY. SOME ENHANCEMENT OF MID TO UPPER-LEVEL FLOW WAS NOTED BY THE 12Z TUCSON AND PHOENIX SOUNDINGS WITHIN THE ERN SEMI-CIRCLE OF THE UPPER LOW. WHEN COUPLED WITH THE MODERATELY UNSTABLE/HIGH PW ENVIRONMENT...THE SETUP MAY FAVOR A FEW INTENSE STORMS CAPABLE OF LOCALLY STRONG WET MICROBURSTS. ..MEAD/LEITMAN.. 09/09/2013 CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z |